Dynamic energy saving mechanism for access points

ABSTRACT

Mobile access points typically run on batteries, and therefore, can operate for a limited amount of time without an external power source. However, because the access point service model requiring the access point to always be available and the access point&#39;s limited battery capacity reduces the time that the mobile access point can be used. Functionality can be incorporated in mobile access points to implement power saving mechanisms by altering the service model that requires the access point to always be available. Configuring the access point to enter into a low powered state for a predefined period of time can conserve mobile access point power and prolong battery life. Functionality for implementing power saving mechanisms can also be incorporated on fixed access points for efficient utilization of computing resources.

RELATED APPLICATION

This application claims the priority benefit of Application No.1177/MUM/2009 filed in India on May 5, 2009.

BACKGROUND

Embodiments of the inventive subject matter generally relate to thefield of wireless communication networks, and more particularly, to adynamic energy saving mechanism for access points.

Access points enable communication devices to connect to and transmitinformation via a communication network. Mobile access points allow forcontinuous connectivity to the communication network (such as theInternet) without being restrained by the coverage area of a fixedaccess point. However, because mobile access points typically run onbatteries, mobile access points can only operate for a limited amount oftime without an external power source. Fixed access points are poweredby an external power source and therefore can provide continuous accessto the communication network without the limitations of using a battery.However, fixed access points can consume a significant amount of power.Energy saving mechanisms can be implemented in mobile access points toimprove battery life, and in fixed access points to reduce powerconsumption (e.g., for green computing).

SUMMARY

Various embodiments are disclosed for reducing power consumption in anaccess point. In one embodiment, the access point receives, from astation, a message indicating a station sleep interval associated withthe station. The station sleep interval indicates a time interval inwhich the station will enter a sleep mode. Access point quietinformation comprising an access point sleep interval is calculatedbased, in part, on the station sleep interval. The access point sleepinterval indicates a time interval in which the access point will entera sleep mode. The access point quiet information is transmitted to thestation to prevent the station from initiating transmissions during theaccess point sleep interval. A start of the access point sleep intervalis determined based on the access point quiet information. The sleepmode in the access point is initiated at the start of the access pointsleep interval.

BRIEF DESCRIPTION OF THE DRAWINGS

The present embodiments may be better understood, and numerous objects,features, and advantages made apparent to those skilled in the art byreferencing the accompanying drawings.

FIG. 1 is an example conceptual diagram illustrating network componentsconfigured to enable energy conservation in an access point;

FIG. 2 illustrates example frame formats for transmission of managementinformation;

FIG. 3 depicts a flow diagram illustrating example operations for anaccess point configuring a quiet interval;

FIG. 4 depicts a flow diagram illustrating example operations for anaccess point configuring a quiet interval;

FIG. 5A is a timing diagram illustrating example transmission operationswhen no stations are connected to an access point;

FIG. 5B is a timing diagram illustrating example transmission operationsfor an access point connected to a station;

FIG. 6 depicts a flow diagram illustrating example operations for astation connected to an access point;

FIG. 7 depicts a flow diagram illustrating example operations for astation connected to an access point; and

FIG. 8 depicts an example wireless device including a mechanism forenergy conservation at access points.

DESCRIPTION OF THE EMBODIMENT(S)

The description that follows includes exemplary systems, methods,techniques, instruction sequences, and computer program products thatembody techniques of the present inventive subject matter. However, itis understood that the described embodiments may be practiced withoutthese specific details. For instance, although some examples refer tomobile phones that can operate as access points, some embodiments mayinclude other types of mobile devices that can operate as access points,fixed access points, or access points that can be powered by either anexternal power source or batteries. For instance, well-known instructioninstances, protocols, structures, and techniques have not been shown indetail in order not to obfuscate the description.

Traditionally, access points have been based on a service model thatrequires the access points to always be available to receivetransmissions from one or more clients (e.g., communicating stations).Mobile access points (e.g., mobile phones behaving as access points) canprovide portability and the ability to connect to a communicationnetwork (e.g., Internet) at any time without the need for access to apower source. However, the access point service model requiring theaccess point to always be available and the access point's limitedbattery capacity reduces the time that the mobile access point can beused. Power saving mechanisms can implemented on the mobile access pointby altering the service model that requires the access point to alwaysbe available. In implementing the power saving mechanisms, the accesspoint can be configured to enter into a low powered state for apredefined period of time based, at least in part, on sleep intervalsassociated with the clients connected to the access point. By operatingin a low powered state during predefined intervals, the mobile accesspoint can conserve power and prolong battery life.

FIG. 1 is an example conceptual diagram illustrating network componentsconfigured to enable energy conservation in an access point. FIG. 1depicts an access point 102 in communication with a station 112 via awireless communication network 116. The access point 102 can be a mobileaccess point or a mobile phone configured to act as an access point. Insome implementations, the access point 102 can also be a fixed accesspoint configured for implementing energy conservation mechanisms, e.g.,for green computing. The access point 102 comprises a transceiver unit106, a power saving unit 108, and processing units 110. The transceiverunit 106 is connected to the power saving unit 108 and the processingunit 110. The power saving unit 108 is also connected to the processingunit 110.

At stage A, the transceiver unit 106 in the access point 102 receives amessage from the station 112 indicating a time interval for which theconnected station 112 will be in sleep mode (“station sleep interval”).In some implementations, where the access point 102 and the connectedstation 112 communicate using IEEE communication protocols, thetransceiver unit 106 can receive, in an Association Request ManagementFrame, one or more parameters (“quiet parameters”) indicating when andfor how long the station will be in the sleep mode. For example, thestation 112 can indicate the quiet parameters by means of a ListenInterval in the Association Request Management Frame. The station entersthe sleep mode, i.e., a low powered state, to conserve energy andpreserve battery life. The station 112 may be connected to the accesspoint 102 or may be attempting to connect to the access point 102.

At stage B, the power saving unit 108 in the access point 102 determineswhen and for how long the access point should quiet the communicationchannel and enter into a sleep mode. The power saving unit 108 cancalculate how long the access point 102 remains in sleep mode based onthe station sleep interval (indicated by the station 112 at stage A).The access point 102 may be connected to a plurality of stations andeach station 112 connected to the access point 102 can be associatedwith a different station sleep interval. In other words, each of theplurality of stations can enter the sleep mode at a different time andremain in the sleep mode for a different period of time. Therefore, thepower saving unit 108 calculates access point quiet information based onwhen and for how long each of the connected stations 112 are in sleepmode. The access point quiet information can indicate a time instant atwhich the access point 102 enters the sleep mode, a time instant atwhich the access point 102 wakes up from the sleep mode, a time intervalfor which the access point 102 is in sleep mode (“access point sleepinterval”), etc. In the example of FIG. 1, the access point 102 is shownconnected to one station 112. Therefore, the access point 102 can quietthe channel, enter the sleep mode, wake up from the sleep mode, allowaccess to the channel, etc. based, at least in part, on the connectedstation's sleep interval. In some implementations, the access point 102can also use other information like the traffic characteristicspecification (TSPEC) from the connected station 112 to determine thequiet parameters. If no stations are connected to the access point 102,the access point 102 can wake up from the sleep mode every beaconinterval, transmit a beacon, wait for a response for a preconfiguredperiod of time, and enter the sleep mode again.

At stage C, the transceiver unit 106 in the access point 102 transmits abeacon, or another suitable message, indicating the access point quietinformation determined at stage B. By transmitting the access pointquiet information, the access point 102 indicates, to each of theconnected stations 112 and other stations that are not connected to theaccess point 102, when and for how long the channel will be quieted andthe access point will be in sleep mode. The access point may also usethe quiet information to indicate when the access point 102 wakes upfrom the sleep mode, exchanges data/management information, and opens upthe communication channel for access. The access point 102 may alsoindicate how often the access point enters sleep mode, how long theaccess point remains in sleep mode, etc. In one implementation, theaccess point 102 can indicate when and for how long the access pointwill be in sleep mode in terms of a beacon interval time period. Forexample, the access point 102 can indicate, in the quiet information,that the access point 102 will enter the sleep mode at the next beaconinterval, wake up after two beacon intervals, remain awake to receiveand transmit information for one beacon interval, and then enter thesleep mode. In another implementation, the access point 102 can use anysuitable time unit (e.g., milliseconds, etc.) to indicate when and forhow long the access point 102 will quiet the communication channel andenter the sleep mode. The station 112 may use the quiet information todetermine how long the communication channel will be available foraccess.

At stage D, the station 112 receives the transmitted beacon. The station112 extracts the transmitted access point quiet information from thereceived beacon. The station 112 can use the beacon for timesynchronization. The station 112 can also use the access point quietinformation to identify when and for how long access to thecommunication channel will be blocked.

At stage E, the station 112 enters the sleep mode. In oneimplementation, a power unit (not shown) in the station 112 maydetermine that the time interval for which the station 112 will be insleep mode has begun. The station 112 may update a station sleep timerwith the station sleep interval. The station may use the station sleeptimer to determine exactly when the station 112 should enter sleep mode.In one implementation, on determining that the station sleep timer hasexpired (e.g., counted down to zero), the power unit may cause thestation 112 to enter the sleep mode. The power unit may direct thestation's transceiver to stop transmitting or receiving signals. Thepower unit may also direct one or more other processing units in thestation 112 to switch to a low powered state to conserve energy.Additionally, before the station enters sleep mode, the station (or thepower unit) can update a “station available timer” with the amount oftime that should elapse before the station wakes up from the sleep mode.

At stage F, the power saving unit 108 in the access point 102 determinesthat the access point 102 should quiet the communication channel andenter a sleep mode. As described with reference to the station 112, inone implementation, the access point 102 can also comprise an accesspoint sleep timer. The power saving unit 108 can monitor the accesspoint sleep timer and direct the access point 102 to enter the sleepmode when the access point sleep timer expires. For example, the powersaving unit 108 can direct the transceiver unit 104 and the otherprocessing units 110 in the access point 102 to switch to a low poweredstate to conserve battery power. While in the sleep mode, the accesspoint 102 may not transmit information to or receive information fromthe stations 112. Thus, by transmitting the access point quietinformation in the beacon (at stage B) to all stations connected to orintending to connect to the access point 102, the access point 102ensures that no station 112 transmits information while the access point102 is in the sleep mode.

At stage G, the power saving unit 108 determines that the communicationchannel should be opened for access. The power saving unit 108 maycomprise a timer indicating how much time should elapse before theaccess point wakes up from sleep mode. When the timer reaches zero, thepower saving unit 108 can trigger the access point 102 (e.g., thetransceiver unit 106 and the processing units 110) to wake from the lowpowered state. In one implementation, the power unit 108 may use theaccess point sleep timer to keep track of 1) how long the access pointshould remain in sleep mode, and 2) when the access point should entersleep mode. In another implementation, the power unit 108 may comprisetwo separate timers, a first timer for determining when the access pointshould enter sleep mode (i.e., the access point sleep timer) and asecond timer for determining when the access point should wake up fromsleep mode.

At stage H, the transceiver unit 104 transmits a beacon on thecommunication channel. The access point 102 wakes up from sleep mode,opens access to the communication channel, and transmits a beacon intime for the connected station 112 to receive the beacon and maintainconnectivity with the access point 102. In transmitting the beacon, theaccess point 102 can indicate that the communication channel isavailable for contention-based access.

At stage I, the station 112 wakes up from the sleep mode. In oneimplementation, on determining that the station available timer hasexpired (e.g., counted down to zero), the power unit can cause thestation 112 to wake up from the sleep mode. The station 112 wakes upfrom sleep mode in time to receive the beacon transmitted by the accesspoint (at stage H) and maintain connectivity with the access point 102.The station 112 can also update the station sleep timer to indicate whenthe station should enter the sleep mode again. The station 112 can alsotransmit data and/or management information (if any) to the access point102.

In one implementation, communication between the access point 102 andthe station 112 may be governed by a set of standards, defined by theInstitute of Electrical and Electronics Engineers (IEEE) 802.11committee, for Wireless Local Area Network (WLAN) communication. TheIEEE 802.11 standards define frame formats for transmission of data andmanagement information. It is noted, however, that in otherimplementations, the communication between the access point 102 and thestation 112 may be governed by other existing or future standards (oramendments to current standards), e.g., 802.16, or by proprietaryprotocols implemented by the network components. FIG. 2 illustratesexample frame formats for transmission of management information. FIG. 2illustrates frame formats for a beacon frame 200, a quiet informationelement (Quiet I.E) 220, and a probe response frame 240 in accordancewith IEEE 802.11 communication standards. An access point (e.g., theaccess point 102 of FIG. 1) can transmit a beacon frame 200 for timesynchronization between one or more connected stations (e.g. station 112of FIG. 1) and the access point 102. The access point 102 can also usethe beacon frame 200 to transmit the access point quiet information andto inform stations if they are to receive data frames from the accesspoint 102. The beacon frame comprises a beacon header 202 and a beaconpayload 220. The beacon header 202 comprises control information (e.g.,frame number) while the beacon payload can comprises information aboutthe communication channel (e.g., channel frequency, a service setidentifier, data rates supported on the communication channel, etc.), abeacon interval (i.e., a time period between transmission of beaconframes), etc.

Additionally, the beacon payload 204 comprises the quiet informationelement (Quiet I.E) 220. The access point 102 can use the Quiet I.E 220to temporarily quiet the communication channel and enter sleep mode toprolong battery life. The Quiet I.E 220 comprises a Quiet I.E header 222and a Quiet I.E payload 224. The Quiet I.E payload 224 comprises a QuietCount 226, a Quiet Period 228, a Quiet Duration 230, and a Quiet Offset232. The Quiet Count 226 indicates a number of target beacontransmission time (TBTT) until the beacon interval during which thequiet interval begins. In other words, the Quiet Count 226 indicateswhen the access point will quiet the communication channel. The QuietPeriod 228 indicates a number of beacon intervals between consecutivequiet intervals (e.g., how often the access point enters sleep mode).The Quiet Duration 230 indicates a time period for which the accesspoint quiets the communication channel and enters sleep mode. The QuietOffset 232 indicates an offset (if any) within a beacon interval whenthe next quiet period will begin (e.g., if the Quiet Duration does notcoincide with the start of a beacon interval).

Additionally, the access point 102 can also transmit the Quiet I.E 220as part of the probe response frame 240. The probe response frame 240comprises a probe response header 242 and a probe response payload 244.The access point 102 transmits a probe response frame 240 in response toa probe request frame from the station scanning the communicationchannels for existing networks and access points. The probe responseframe 240 comprises information similar to the beacon frame 200. Theprobe response payload 244 comprises the Quiet I.E 220 along with otherinformation such as channel frequency, the service set identifier, datarates supported on the communication channel, etc.

FIG. 3 and FIG. 4 depict a flow diagram illustrating example operationsfor an access point configuring a quiet interval. Flow 300 begins atblock 302 in FIG. 3.

At block 302, a message is received from a station indicating a timeinterval for which the station will be in sleep mode (“station sleepinterval”). For example, the station 112 of FIG. 1 may indicate, to theaccess point 102, how often the station will wake up from sleep mode toreceive frames from the access point, when the station will enter thesleep mode, etc. In one implementation, the access point can be mobilephone acting as an access point. In another implementation, the accesspoint can be a fixed access point. It is noted, however, that in otherimplementations the access point can be other types of access pointsthat can operate using either battery power or an external power source.In one implementation, a station complying with IEEE 802.11communication standards may indicate how often the station listens (onthe communication channel) for beacon frames in a Listen Interval in anAssociation Request Management Frame. The Listen Interval is typicallyindicated as a number of beacon intervals for which the station will bein the sleep mode. For example, a station with a Listen Interval of 2will receive only alternate beacons (i.e., the station will be in thesleep mode for two beacon intervals). The access point may receiveAssociation Request Management Frames (or other messages indicating atime instant and/or the time interval for which the station will be insleep mode) from one or more stations connected to or intending toconnect to the access point. The flow continues at block 304.

At block 304, the message indicating the station sleep interval isanalyzed to determine access point quiet information. For example, thepower saving unit 108 in the access point 102 can analyze the messagereceived (at block 302) to determine the access point quiet information(e.g., access point sleep interval, when the access point wakes up fromthe sleep mode, etc). As described earlier, stations operating in apower save mode typically go to sleep to conserve power and wakeup onlyfor a predetermined number of beacon intervals. The access point can useinformation indicating when and for how long the station goes to sleep(as indicated, e.g., in the Listen Interval) to determine when and forhow long the access point can lock the communication channel and enter asleep mode. For example, if a station connected to the access pointwakes up every fifth beacon interval, it may be sufficient for theaccess point to wakeup just before the start of the fifth beaconinterval and transmit a beacon frame in time for the connected stationto receive the beacon frame. If there are multiple stations connected tothe access point, the access point can calculate a least common factorof the station sleep interval (e.g., the Listen Interval) associatedwith each of the connected stations and accordingly determine when towake up from sleep mode. For example, if three stations with ListenIntervals 3, 6, and 9 respectively are connected to the access point,then the access point may transmit a beacon once every three (the leastcommon factor of 3, 6, and 9 is 3) beacon intervals to ensure that thestations remain connected to the access point. After the access pointdetermines the access point quiet information, the flow continues atblock 306.

At block 306, a beacon frame comprising the access point quietinformation is generated. For example, the access point 102 may generatethe beacon frame. In one implementation, the beacon frame may be in theformat described with reference to FIG. 2 (see beacon frame 200 of FIG.2). The access point may also indicate the access point quietinformation in a probe response frame (e.g., the probe response frame240 of FIG. 2). In another implementation, the access point may notifythe stations of the access point quiet information using other suitablemessage formats. The flow continues at block 308.

At block 308, the beacon frame (generated at block 306) is transmittedon the communication channel. The beacon frame is transmitted to all thestations listening on the communication channel. The beacon ensures thatstations that are connected to the access point remain connected to andare in synchronization with the access point. In transmitting thebeacon, the access point can advertise its presence and inform stationslistening on the communication channel of the access point'scapabilities (e.g., access point identifier, data rates supported, etc).As described earlier, the beacon frame is also used to transmit theaccess point quiet information and notify the stations of when and forhow long the communication channel will be quieted. By transmitting theaccess point quiet information, the access point can control access tothe communication channel during the time the access point is in sleepmode. Thus, the access point can also control transmissions from theconnected stations to the access point. The flow continues at block 310in FIG. 4 (see connector A).

At block 310, it is determined whether there exists information to betransmitted to the connected stations. The access point may access abuffer comprising pending data frames to be transmitted to determine ifthere exists data to be transmitted to the connected stations. In someimplementations, the access point may also transmit managementinformation to connected stations and/or stations that wish to connectto the access point. For example, the access point may determine that anassociation response frame should be transmitted in response to thestation transmitting an association request frame to connect to theaccess point's network. If it is determined that there existsinformation to be transmitted to the stations, the flow continues atblock 320. Otherwise, the flow continues at block 312.

At block 320, the information is transmitted to the stations. Forexample, the access point 102 may transmit data frames to the connectedstation 112. In some implementations, the access point may determinewhether there is sufficient time for data transmission before thestations and the access point enter a sleep mode. In one example, theaccess point may access an access point sleep timer and determine theamount of time remaining until the access point quiets the communicationchannel and enters the sleep mode. The access point can calculate theamount of time required for data transmission based on data rate, framelength, etc. If the access point determines that the stations will beawake to receive all the data to be transmitted, the access pointtransmits the data. Otherwise, the access point can buffer framesdestined for the connected stations and alert the stations (e.g., via abeacon, a traffic indication map (TIM), etc.) when the stations and theaccess point wake up from sleep mode. The flow continues at block 312.

At block 312, it is determined whether a station is transmittinginformation. The station (e.g., the station 112) may transmit data ormanagement information to the access point (e.g., the access point 102).For example, a station connected to the access point may transmit one ormore data frames. As another example, a station connected to the accesspoint may transmit a disassociation frame to the access point toterminate a connection with the access point. As another example, astation trying to connect to the access point may transmit anAssociation Request frame to request a connection with the access point.The stations can transmit data and management information using othersuitable communication protocols. If it is determined that the stationis transmitting data, the flow continues at block 322. Otherwise, theflow continues at block 314.

At block 322, information is received from the stations. For example,the access point 102 of may receive data and/or management informationfrom the station 112. The flow continues at block 314.

At block 314, it is determined whether the access point should enter thesleep mode. For example, the power saving unit 108 in the access point102 may determine that the access point should enter the sleep mode. Asdescribed earlier, the access point may comprise an access point sleeptimer indicating the amount of time that should elapse before the accesspoint quiets the communication channel and enters sleep mode. The powersaving unit 108 may trigger one or more operating units (e.g., atransceiver unit, etc.) in the access point to enter the sleep mode whenthe value of the access point sleep timer reaches zero. If it determinedthat the access point should enter sleep mode, the flow continues atblock 316. Otherwise, the flow continues at block 310, where the accesspoint determines whether there is data to be transmitted to or data tobe received from a station.

At block 316, the access point enters the sleep mode. For example, thepower saving unit 108 in the access point 102 may direct the transceiverunit 106 and other processing units 110 in the access point 102 toswitch to a low powered state to conserve battery power. Before theaccess point enters the sleep mode, the access point also quiets thecommunication channel (i.e., locks access to the communication channel).The stations connected to the access point set a station timer (e.g., anetwork allocation vector (NAV) timer) indicating a time (e.g., QuietDuration 230 from the Quiet I.E 220 of FIG. 2) that should elapse beforethe access point wakes up from sleep mode. After the stations update thestation timer, the communication channel is locked. By locking thecommunication channel before entering sleep mode, the access pointensures that stations do not transmit data or management frames to theaccess point when the access point is in sleep mode. A timer may also beupdated to indicate the time (e.g., Quiet Duration 230 of FIG. 2) thatshould elapse before the access point wakes up from sleep mode. Fromblock 416, the flow ends.

After the access point wakes up from sleep mode, the access point opensthe communication channel for contention-based access and transmits thebeacon. The access point also transmits data and/or management framesthat it has for the connected stations and remains awake for apredetermined time interval to receive any data and/or management framesfrom the connected stations or stations that wish to connect to theaccess point. The access point then locks access to the communicationchannel and enters the sleep mode again.

The various time intervals associated with the access point configuredfor energy conservation are further described using timing diagrams 5Aand 5B. FIG. 5A is a timing diagram 500 illustrating exampletransmission operations when no stations are connected to the accesspoint. Time interval 502 indicates the interval during which the accesspoint (e.g., access point 102) is awake. Stations (e.g., station 112)can communicate with the access point during the interval 502. Forexample, a station may detect a beacon 510 transmitted by the accesspoint and transmit an Association Request frame to request a connectionto the access point. Time interval 504 indicates an interval duringwhich the access point is in sleep mode. The sleep mode is a low powerstate, which the access point enters to conserve energy and enhancebattery life. The access point transmits a Quiet Information Element(Quiet I.E) in the beacons or probe response frames (transmitted inresponse to the probe request frames) during time interval 502 (i.e.,before the access point enters sleep mode). The access point uses theQuiet I.E to indicate when and for how long the access point will be insleep mode (i.e., the time interval 504). In other words, the accesspoint locks the communication channel for the interval indicated by thetime interval 504 and does not receive communications from or transmitcommunications to other stations.

Arrowhead 510 indicates a time instant at which the access point wakesup (e.g., just before a predetermined target beacon transmission time(TBTT)) to transmit the beacon. Arrowhead 512 indicates a time instantat which the Quiet Offset (as indicated in the Quiet I.E.) begins andthe access point enters the sleep mode. Thus, the quiet time interval504 repeats every beacon interval 508. Because the access point is notconnected to any station, the access point wakes up every beaconinterval 508 (which is the sum of time intervals 502 and 504) totransmit the beacon as depicted by arrowheads 510 and 514. Likewise, theaccess point enters sleep mode every beacon interval (see arrowheads 512and 516).

In one implementation, the access point configures the Quiet I.E frame(see Quiet I.E frame format 220 in FIG. 2) by assigning a Quiet Count518 of 1 beacon interval and a Quiet Period of 1 indicating that thequiet period starts at the next TBTT (denoted by arrowhead 510) and thatthe quiet period repeats every beacon interval. The access point canalso configure the quiet duration to time interval 504 indicating thatthe communication channel should be quiet for the time period indicatedby time interval 504. Likewise, the access point can configure the quietoffset to time interval 502 indicating that the quiet period startsafter time interval 502.

FIG. 5B is a timing diagram 550 illustrating example transmissionoperations for an access point connected to a station. In the exampleshown in FIG. 5B, the connected station (e.g., the station 112) isconnected to the access point (e.g., the access point 102) with a ListenInterval (indicated in an Association Request Management Frame) of twobeacon intervals. The connected station uses the Listen Interval toindicate to the access point that the station will wake up every secondbeacon interval to listen for beacons (for synchronization) from andexchange data and/or management information with the access point.

Time interval 552 indicates the interval during which the access pointis awake. The access point and the connected station can exchange dataand management frames during this interval. For example, the connectedstation may transmit a data frame to the access point. As anotherexample, the access point can indicate to a station (e.g., bytransmitting a Traffic Indication Map (TIM)) if the access point hasdata/management frames for the station. New stations (stations that arenot connected to the access point) can also communicate with the accesspoint during the interval 552. For example, a station may detect abeacon transmitted by the access point during the time interval 552 andtransmit an Association Request frame to request a connection to theaccess point. Time interval 554 indicates an interval during which theaccess point is in sleep mode.

With reference to the Quiet I.E. frame structure 220 depicted in FIG. 2,the access point can configure the Quiet I.E frame based on thestation's Listen Interval (two beacon intervals). The access point canconfigure the Quiet I.E with a Quiet Count 570 of 1 beacon interval anda Quiet Period 572 of 2 beacon intervals indicating that the quietperiod starts at the next TBTT (see arrowhead 560) and that the quietperiod repeats every second beacon interval (see arrowhead 564). Theaccess point can also configure the Quiet Duration to time interval 554indicating that the communication channel should be quiet for the timeperiod indicated by time interval 554. Likewise, the access point canconfigure the Quiet Offset to time interval 552 indicating that thequiet period starts after time interval 552.

Arrowhead 560 indicates a time instant at which the access point wakesup (e.g., just before the TBTT) to transmit the beacon. Arrowhead 562indicates a time instant at which the Quiet Offset (as indicated in theQuiet I.E.) begins and the access point enters the sleep mode. Asdepicted by arrowheads 560 and 564, the access point wakes up everysecond beacon interval 558 to transmit beacons, probe responses, dataframes, etc. Also, as depicted by arrowheads 562 and 566, the quietduration 554 repeats every second beacon interval 558.

It should be noted that the time intervals during which the access pointis awake and in sleep mode and the beacon interval are configurable. Theuser can configure any one or all of the time intervals depending on thetype and nature of the traffic that is estimated to pass through theaccess point. Additionally, the user may also configure the access pointto dynamically configure the time intervals that the access point isawake and in sleep mode based on the traffic handled by the accesspoint.

FIG. 6 and FIG. 7 depict a flow diagram illustrating example operationsfor a station connected to an access point. Flow 600 begins at block 602in FIG. 6.

At block 602, a time interval for which the station will be in sleepmode is provided to an access point. For example, the station 112 maysend a message indicating to the access point 102 a number of beaconintervals it intends to spend in sleep mode. In one implementation, thestation can indicate a station sleep interval (i.e., the number ofintervals the station will be in sleep mode) by configuring a Listeninterval in an Association Request Management frame. In someimplementations, the station sleep interval may not be described asmultiples of the beacon interval. Instead, the station may use anysuitable unit of time (e.g., seconds, milliseconds, etc.) to indicatethe station sleep interval and a time interval at which the stationsleep interval repeats (if applicable). Also, the station may use anysuitable message format and/or frame format (agreed upon by the accesspoint and the station) to communicate with the access point. The flowcontinues at block 604.

At block 604, a beacon comprising access point quiet information isreceived from the access point. For example, the station 112 receives abeacon (e.g., the beacon frame 200 of FIG. 2) from the access point 102.As described in FIG. 3 (see discussion for blocks 302 and 304), in oneimplementation, the access point can receive Association RequestManagement frames indicating Listen Intervals from a plurality ofconnected stations. The access point can calculate an access point quietinterval from the received Listen Intervals and transmit the accesspoint quiet interval as part of the quiet information in a beacon frame.During the access point quiet interval, the access point can enter thesleep mode and block access to the communication channel. The flowcontinues at block 606.

At block 606, the access point quiet information is retrieved from thebeacon received at block 604. For example, the station 102 may processthe received beacon to extract the access point quiet information. Inone implementation, the station may extract the quiet informationelement (e.g., the Quiet I.E 220 of FIG. 2) from the beacon to determinewhen the quiet duration starts, the length of the quiet duration, whendata and management information can be transmitted, etc. The stationscan also update a Network Allocation Vector (NAV) timer with the QuietDuration (i.e., the Quiet duration 230 of FIG. 2) indicated in the QuietInformation Element. The NAV timers count down so that the stations wakeup in time to receive the beacon transmitted by the access point. Inanother implementation, the station may retrieve the access point sleepinterval from the access point quiet information (transmitted using anysuitable message format and communication protocol) and accordinglyupdate a station available timer. The flow continues at block 608.

At block 608, it is determined whether the communication medium isavailable. For example, for contention-based communication channelaccess, the station 112 may transmit a request-to-send (RTS) frame onthe communication channel to the access point 102 to determine if thecommunication medium is available. The station may also indicate anamount of time for which the communication channel will be in use. Theaccess point may transmit a clear-to-send (CTS) signal to one of thestations contending for the communication channel to indicate that thecommunication channel is available for transmission. Other stations mayalso receive the RTS/CTS signal and refrain from accessing thecommunication channel during the time interval when another station istransmitting. If it is determined that the communication medium isavailable for data transmission, the flow continues at block 610.Otherwise, the flow continues at block 611.

At block 611, on determining that the communication medium is notavailable for transmission, the station waits for a specified period oftime. In the contention-based channel access example described withreference to block 608, other stations that do not receive permission totransmit along the communication channel also receive the RTS/CTSframes. The stations can update a timer and wait until the transmittingstation has released the communication channel. In one implementation,the station may wait for a random amount of time before it senses thecommunication channel to avoid frame collision. In anotherimplementation, the station waits for the period of time specified in anRTS frame transmitted by a station that is currently transmitting. Theflow continues at block 608, where, after the specified period of time,the station senses the communication channel to determine whether thecommunication channel is available.

At block 610, a time period required to transmit information(“transmission time”) to the access point is calculated. For example,the station 112 may calculate the time period required for transmissionof a data/management frame to the access point 102. The transmissiontime may be calculated based on a number of bytes of data to betransmitted, frame size, the capacity and data rate of the communicationchannel, the network traffic, a network model, etc. The flow continuesat block 612 in FIG. 7.

At block 612, it is determined whether the transmission time is greaterthan the time before the communication channel is quieted. In otherwords, it is determined whether there is sufficient time to transmitinformation to the access point before the access point quiets thecommunication channel and enters sleep mode. In a communicationenvironment using IEEE communication protocols, it may be determinedwhether there is sufficient time to transmit information to the accesspoint before the start of the next Quiet Duration (e.g., the QuietDuration 230 of FIG. 2). For example, the transmission time may becompared with an amount of time indicated by a station sleep timer.Stations that are not connected to the access point may determinewhether the transmission time is greater than the time that shouldelapse before the access point locks the communication channel andenters a sleep mode. If it is determined that the time required for datatransmission is greater than the time before the communication channelis quieted, the flow continues at block 614. Otherwise, the flowcontinues at block 624.

At block 624, the data is transmitted to the access point. The stationconnected to the access point transmits information in response to thestation determining that the transmission time is less than the amountof time that should elapse before the access point quiets thecommunication channel and enters sleep mode (e.g., before the start ofthe Quiet Duration). A station that is not connected to the access pointtransmit information to the access point in response to the stationdetermining that the transmission time is less than the amount of timethat should elapse before the access point quiets the communicationchannel. The station can transmit a data frame or a management frame tothe access point. For example, a station may transmit a Probe RequestFrame to scan for an existing and compatible access point, a data frameto transmit data to a second station via the access point, etc. The flowcontinues at block 616.

At block 614, information is prevented from being transmitted to theaccess point. The flow 600 moves from block 612 to block 614 if it isdetermined that the transmission time is greater than the time beforethe access point quiets the communication channel and enters sleep mode(e.g., before the start of the Quiet Duration). For example, the station112 prevents the transmission of data and/or management information tothe access point 102 in response to the station determining that thetransmission time is greater than the time before the start of the QuietDuration. The information to be transmitted may be stored (e.g., in abuffer frame) and may be transmitted when the station wakes up from thesleep mode. In another implementation, stations that are not connectedto the access point may store information to be transmitted and maytransmit the information (e.g., management frames requestingconnectivity) when the access point wakes up from the sleep mode andopens access to the communication channel. After the station determineswhether it should transmit information (see block 624) or preventtransmission of the information (see block 614), the flow continues atblock 616.

At block 616, it is determined whether the station should enter sleepmode. As described earlier, the stations may update a local timer withthe amount of time that should elapse before the station enters sleepmode. In one implementation, the station sleep timer may count down,triggering the station to enter sleep mode when the counter reacheszero. If it is determined that the station should enter sleep mode, theflow continues at block 626. Otherwise, the flow continues at block 622.

At block 622, it is determined whether there is any information to betransmitted. For example, the station 122 may determine whether thereexist any data and/or management frames to be transmitted to the accesspoint 102. If the station determines that there exists information thatshould be transmitted to the access point, the flow continues at block608 in FIG. 6 where the station determines whether the communicationchannel is available. Otherwise, the flow continues at block 616 wherethe station determines whether it should enter sleep mode.

At block 626, the station enters sleep mode. As described earlier, thestations may update a station available timer with the amount of timethat the communication channel is quieted and the access point is in thesleep mode, as indicated by the access point. In one implementation, thestation 112 may update its NAV timer with the Quiet Duration 230indicated in the Quiet I.E 220 of FIG. 2. As the stations are in thesleep mode, the NAV timer counts down triggering the stations to wake upwhen the NAV timer reaches zero. In some implementations, the stationsmay use any suitable counter/timer to indicate when stations can enteror wake up from the sleep mode. From block 626, the flow ends.

It should be understood that the depicted flow diagrams (FIGS. 3, 4, 6,and 7) and the timing diagram (FIG. 5) are examples meant to aid inunderstanding embodiments and should not be used to limit embodiments orlimit scope of the claims. Embodiments may perform additionaloperations, fewer operations, operations in a different order,operations in parallel, and some operations differently. For example,FIG. 7 describes the station determining whether there is sufficienttime for transmission before the communication channel is quieted (seeblock 612). However, in some implementations, the onus to determinewhether the station should be allowed to transmit may be on the accesspoint. For example, the station may transmit an RTS signal to the accesspoint indicating the frame length, transmission time, etc. The accesspoint may determine that the transmission time is greater than the timebefore the access point quiets the communication channel. The accesspoint may prevent the station from transmitting information.

Also, because the access point is awake and can transmit/receive dataand/or management information for only a predefined period of time,there may be a trade-off between the access point's performance andpower saving for prolonged battery life. In some implementations, theaccess point can be configured to operate in full power mode when one ormore stations are connected to the access point. The access point mayenter into power saving mode (i.e., sleep mode) and wake up for alimited time interval when there are no stations connected to the accesspoint.

As described above, in some embodiments, the access point is configuredto quiet the communication medium (i.e., the communication channel) bytransmitting a quiet information element (Quiet I.E.) in the beaconframe and/or a probe response frame. However, in some implementations,the access point and/or one or more of the connected stations may notsupport receiving the Quiet I.E. In some implementations, the accesspoint can quiet the communication channel using a CTS (Clear-to-Send) toself scheme. The CTS-to-self scheme is a generic scheme that isrecognized by all clients (e.g., connected stations, transmittingstations, mobile phones, access points, etc.) implementing IEEE 802.11communication standards. A CTS signal indicates a duration for which astation is allowed to transmit data on the communication channel. TheCTS signal also indicates, to other stations, the duration for which thecommunication channel will be busy and therefore, should not beaccessed. The access point can transmit a CTS signal to itselfindicating a time interval for which the communication channel will belocked (e.g., the Quiet Duration, the access point sleep interval, etc).The CTS signal, which is also received by other stations, indicates theother stations should not access the communication channel for theindicated time interval. The access point can enter the sleep mode ontransmitting the CTS signal. This can ensure that no station transmitsdata or management frames to the access point while the access point isin the sleep mode. This also ensures that no data or managementinformation is lost while the access point is in sleep mode.

Embodiments may take the form of an entirely hardware embodiment, anentirely software embodiment (including firmware, resident software,micro-code, etc.) or an embodiment combining software and hardwareaspects that may all generally be referred to herein as a “circuit,”“module” or “system”. Furthermore, embodiments of the inventive subjectmatter may take the form of a computer program product embodied in anytangible medium of expression having computer usable program codeembodied in the medium. The described embodiments may be provided as acomputer program product, or software, that may include amachine-readable medium having stored thereon instructions, which may beused to program a computer system (or other electronic device(s)) toperform a process according to embodiments, whether presently describedor not, since every conceivable variation is not enumerated herein. Amachine-readable medium includes any mechanism for storing ortransmitting information in a form (e.g., software, processingapplication) readable by a machine (e.g., a computer). Themachine-readable medium may include, but is not limited to, magneticstorage medium (e.g., floppy diskette); optical storage medium (e.g.,CD-ROM); magneto-optical storage medium; read only memory (ROM); randomaccess memory (RAM); erasable programmable memory (e.g., EPROM andEEPROM); flash memory; or other types of medium suitable for storingelectronic instructions. In addition, embodiments may be embodied in anelectrical, optical, acoustical or other form of propagated signal(e.g., carrier waves, infrared signals, digital signals, etc.), orwireline, wireless, or other communications medium.

Computer program code for carrying out operations of the embodiments maybe written in any combination of one or more programming languages,including an object oriented programming language such as Java,Smalltalk, C++ or the like and conventional procedural programminglanguages, such as the “C” programming language or similar programminglanguages. The program code may execute entirely on a user's computer,partly on the user's computer, as a stand-alone software package, partlyon the user's computer and partly on a remote computer or entirely onthe remote computer or server. In the latter scenario, the remotecomputer may be connected to the user's computer through any type ofnetwork, including a local area network (LAN), a personal area network(PAN), or a wide area network (WAN), or the connection may be made to anexternal computer (for example, through the Internet using an InternetService Provider).

FIG. 8 depicts an example wireless device e.g., WLAN device 800. In oneimplementation, the WLAN device 800 may be a WLAN station (e.g., station112 of FIG. 1). In another implementation, the WLAN device 800 may be anaccess point operating in an 802.11 WLAN communication environment(e.g., access point 102 of FIG. 1). The WLAN device 800 includes aprocessor unit 802 (possibly including multiple processors, multiplecores, multiple nodes, and/or implementing multi-threading, etc.). TheWLAN device 800 includes a memory unit 806. The memory unit 806 may besystem memory (e.g., one or more of cache, SRAM, DRAM, zero capacitorRAM, Twin Transistor RAM, eDRAM, EDO RAM, DDR RAM, EEPROM, NRAM, RRAM,SONOS, PRAM, etc.) or any one or more of the above already describedpossible realizations of machine-readable media. The WLAN device 800also includes a bus 810 (e.g., PCI, ISA, PCI-Express, HyperTransport®,InfiniBand®, NuBus, etc.), and network interfaces 804 that include atleast one wireless network interface (e.g., a WLAN interface, aBluetooth® interface, a WiMAX interface, a ZigBee® interface, a WirelessUSB interface, etc.). The WLAN device 800 also includes a power savingunit 808. The power saving unit 808 comprises functionality forconserving power to prolong battery life in an access point described inaccordance with FIGS. 1-7.

Any one of the above-described functionalities may be partially (orentirely) implemented in hardware and/or on the processing unit 802. Forexample, the functionality may be implemented with an applicationspecific integrated circuit, in logic implemented in the processing unit802, in a co-processor on a peripheral device or card, etc. Further,realizations may include fewer or additional components not illustratedin FIG. 8 (e.g., additional network interfaces, peripheral devices,etc.). The processor unit 802 and the network interfaces 804 are coupledto the bus 810. Although illustrated as being coupled to the bus 810,the memory 806 may be coupled to the processor unit 802.

While the embodiments are described with reference to variousimplementations and exploitations, it will be understood that theseembodiments are illustrative and that the scope of the inventive subjectmatter is not limited to them. In general, the dynamic energy savingmechanism for access points as described herein may be implemented withfacilities consistent with any hardware system or hardware systems. Manyvariations, modifications, additions, and improvements are possible.

Plural instances may be provided for components, operations, orstructures described herein as a single instance. Finally, boundariesbetween various components, operations, and data stores are somewhatarbitrary, and particular operations are illustrated in the context ofspecific illustrative configurations. Other allocations of functionalityare envisioned and may fall within the scope of the inventive subjectmatter. In general, structures and functionality presented as separatecomponents in the exemplary configurations may be implemented as acombined structure or component. Similarly, structures and functionalitypresented as a single component may be implemented as separatecomponents. These and other variations, modifications, additions, andimprovements may fall within the scope of the inventive subject matter.

What is claimed is:
 1. A method for reducing power consumption in anaccess point, the method comprising: receiving a message at the accesspoint from a first station, via a wireless communication channel,indicating a first station sleep interval associated with the firststation, wherein the first station sleep interval indicates a timeinterval in which the first station will enter a sleep mode; calculatinga first access point quiet information comprising a first access pointsleep interval based, at least in part, on the first station sleepinterval, wherein the first access point sleep interval indicates a timeinterval in which the access point will enter a sleep mode; transmittingto the first station, via the wireless communication channel, a beaconindicating the first access point quiet information to prevent the firststation from initiating transmissions to the access point during thefirst access point sleep interval; determining, based on the firstaccess point quiet information, a start of the first access point sleepinterval; and initiating the sleep mode in the access point at the startof the first access point sleep interval.
 2. The method of claim 1,wherein the first access point quiet information further comprises oneor more of a time instant at which the access point enters the sleepmode, a time instant at which the access point wakes up from the sleepmode, and an indication of how often the access point enters the sleepmode.
 3. The method of claim 1, further comprising: detecting, at theaccess point, a pending transmission associated with the first station,wherein the pending transmission comprises one of a data frametransmission and a management frame transmission; calculating atransmission time associated with the pending transmission; comparingthe transmission time with an amount of time remaining before the firstaccess point sleep interval begins; determining that the transmissiontime is greater than the amount of time remaining before the firstaccess point sleep interval begins; and preventing execution of thepending transmission associated with the first station.
 4. The method ofclaim 1, wherein the access point is a mobile phone access point.
 5. Themethod of claim 1, wherein said calculating the first access point quietinformation comprises calculating the first access point sleep intervalthat initiates the sleep mode in the access point during the firststation sleep interval.
 6. The method of claim 1, further comprising:determining that no stations are connected to the access point, via thewireless communication channel; calculating a second access point quietinformation comprising a second access point sleep interval based, atleast in part, on a beacon interval and on said determining that nostations are connected to the access point, wherein the beacon intervalindicates a time interval in which a beacon is transmitted, and whereinthe second access point sleep interval indicates a time interval inwhich the access point will enter a sleep mode; transmitting, via thewireless communication channel, a second beacon indicating the secondaccess point quiet information to prevent one or more stations frominitiating transmissions to the access point during the second accesspoint sleep interval; determining, based on the second access pointquiet information, a start of the second access point sleep interval;initiating the sleep mode in the access point at the start of the secondaccess point sleep interval; determining, based on the second accesspoint quiet information, an end of the second access point sleepinterval; and initiating a normal operational mode, at the access point,in response to determining the end of the second access point sleepinterval.
 7. The method of claim 1, further comprising: receiving asecond message at the access point from a second station, via thewireless communication channel, indicating a second station sleepinterval associated with the second station, wherein the second stationsleep interval indicates a time interval in which the second stationwill enter a sleep mode; calculating a second access point quietinformation comprising a second access point sleep interval based, atleast in part, on the first station sleep interval and the secondstation sleep interval, wherein the second access point sleep intervalindicates a time interval for which the access point will enter a sleepmode; and transmitting to the first and the second stations, via thewireless communication channel, a second beacon indicating the secondaccess point quiet information to prevent the first and the secondstations from initiating transmissions to the access point during thesecond access point sleep interval.
 8. The method of claim 7, whereinsaid calculating the second access point quiet information comprises:determining a least common factor between the first station sleepinterval associated with the first station and the second station sleepinterval associated with the second station; and determining when toinitiate the second access point sleep interval based, at least in part,on said determining the least common factor between the first stationsleep interval associated with the first station and the second stationsleep interval associated with the second station.
 9. A methodcomprising: receiving access point quiet information at a station froman access point, via a wireless communication channel, wherein theaccess point quiet information comprises an access point sleep intervalindicating a time interval for which the access point will enter a sleepmode; determining that the wireless communication channel is availablefor transmission of information to the access point, wherein thetransmission of information comprises one of a data frame transmissionand a management frame transmission; calculating a transmission timeassociated with the transmission of information to the access point;comparing the transmission time with an amount of time remaining beforea station sleep interval associated with the station begins, wherein thestation sleep interval indicates a time interval in which the stationwill enter a sleep mode; determining that the transmission time is lessthan the amount of time that remains before the station sleep intervalbegins; and transmitting the information to the access point.
 10. Themethod of claim 9, further comprising: transmitting, to the accesspoint, the station sleep interval associated with the station, whereinthe access point sleep interval is determined based, in part, on thestation sleep interval.
 11. The method of claim 9, further comprising:determining, based on the station sleep interval, a start of the stationsleep interval; and initiating the sleep mode in the station at thestart of the station sleep interval.
 12. The method of claim 11, whereinsaid determining, based on the station sleep interval, the start of thestation sleep interval further comprises: determining that a stationsleep timer associated with the station is expired, wherein the stationsleep timer indicates an amount of time that remains before the stationenters the sleep mode.
 13. The method of claim 12, further comprising:storing, in a network allocation vector timer, associated with thestation, the access point sleep interval, wherein the network allocationvector timer indicates an amount of time that remains before the stationwakes up from the sleep mode; determining that the network allocationvector timer associated with the station has expired; and initiating anormal operational mode, at the station, in response to determining thatthe network allocation vector timer associated with the station hasexpired.
 14. An access point device comprising: a processor unit; atransceiver unit coupled with the processor unit, the transceiver unitconfigured to receive a message from a first station, via a wirelesscommunication channel, indicating a first station sleep intervalassociated with the first station, wherein the first station sleepinterval indicates a time interval in which the first station will entera sleep mode; and a power saving unit coupled with the processor unit,the power saving unit configured to: calculate a first access pointquiet information comprising a first access point sleep interval based,at least in part, on the first station sleep interval, wherein theaccess point sleep interval indicates a time interval in which theaccess point device will enter a sleep mode; transmit to the firststation, via the wireless communication channel, a beacon indicating thefirst access point quiet information to prevent the first station frominitiating transmissions to the access point device during the firstaccess point sleep interval; determine, based on the first access pointquiet information, a start of the first access point sleep interval; andinitiate the sleep mode in the access point device at the start of thefirst access point sleep interval.
 15. The access point device of claim14, wherein the first access point quiet information further comprisesone or more of a time instant at which the access point device entersthe sleep mode, a time instant at which the access point device wakes upfrom the sleep mode, and an indication of how often the access pointdevice enters the sleep mode.
 16. The access point device of claim 14,further comprising: the transceiver unit configured to: detect a pendingtransmission associated with the first station, wherein the pendingtransmission comprises one of a data frame transmission and a managementframe transmission; the power saving unit configured to: calculate atransmission time associated with the pending transmission; compare thetransmission time with an amount of time remaining before the firstaccess point sleep interval begins; determine that the transmission timeis greater than the amount of time remaining before the first accesspoint sleep interval begins; and prevent execution of the pendingtransmission associated with the first station.
 17. The access pointdevice of claim 14, wherein the power saving unit configured tocalculate the first access point quiet information further comprises thepower saving unit configured to calculate the first access point sleepinterval that initiates the sleep mode in the access point device duringthe first station sleep interval.
 18. The access point device of claim14, further comprising: the power saving unit configured to determinethat no stations are connected to the access point device, via thewireless communication channel; calculate a second access point quietinformation comprising a second access point sleep interval based, atleast in part, on a beacon interval and on said determining that nostations are connected to the access point device, wherein the beaconinterval indicates a time interval in which a beacon is transmitted, andwherein the second access point sleep interval indicates a time intervalin which the access point device will enter a sleep mode; transmit, viathe wireless communication channel, a second beacon indicating thesecond access point quiet information to prevent one or more stationsfrom initiating transmissions to the access point device during thesecond access point sleep interval; determine, based on the secondaccess point quiet information, a start of the second access point sleepinterval; initiate the sleep mode in the access point device at thestart of the second access point sleep interval; determine, based on thesecond access point quiet information, an end of the second access pointsleep interval; and initiate a normal operational mode, at the accesspoint device, in response to determining the end of the second accesspoint sleep interval.
 19. The access point device of claim 14, furthercomprising: the transceiver unit configured to: receive a second messagefrom a second station, via the wireless communication channel,indicating a second station sleep interval associated with the secondstation, wherein the second station sleep interval indicates a timeinterval in which the second station will enter a sleep mode; the powersaving unit configured to: calculate a second access point quietinformation comprising a second access point sleep interval based, atleast in part, on the first station sleep interval and the secondstation sleep interval, wherein the second access point sleep intervalindicates a time interval for which the access point device will enter asleep mode; and transmit to the first and the second stations, via thewireless communication channel, a second beacon indicating the secondaccess point quiet information to prevent the first and the secondstations from initiating transmissions to the access point device duringthe second access point sleep interval.
 20. The access point device ofclaim 19, wherein the power saving unit configured to calculate thesecond access point quiet information comprises the power saving unitconfigured to: determine a least common factor between the first stationsleep interval associated with the first station and the second stationsleep interval associated with the second station; and determine when toinitiate the second access point sleep interval based, at least in part,on said determining the least common factor between the first stationsleep interval associated with the first station and the second stationsleep interval associated with the second station.
 21. One or morenon-transitory machine-readable storage media, having instructionsstored therein, which when executed by one or more processors causes theone or more processors to perform operations that comprise: receiving amessage at an access point from a first station, via a wirelesscommunication channel, indicating a first station sleep intervalassociated with the first station, wherein the first station sleepinterval indicates a time interval in which the first station will entera sleep mode; calculating a first access point quiet informationcomprising a first access point sleep interval based, at least in part,on the first station sleep interval, wherein the first access pointsleep interval indicates a time interval in which the access point willenter a sleep mode; transmitting to the first station, via the wirelesscommunication channel, a beacon indicating the first access point quietinformation to prevent the first station from initiating transmissionsto the access point during the first access point sleep interval;determining, based on the first access point quiet information, a startof the first access point sleep interval; and initiating the sleep modein the access point at the start of the first access point sleepinterval.
 22. The machine-readable storage media of claim 21, whereinthe first access point quiet information further comprises one or moreof a time instant at which the access point enters the sleep mode, atime instant at which the access point wakes up from the sleep mode, andan indication of how often the access point enters the sleep mode. 23.The machine-readable storage media of claim 21, wherein the operationsfurther comprise: detecting, at the access point, a pending transmissionassociated with the first station, wherein the pending transmissioncomprises one of a data frame transmission and a management frametransmission; calculating a transmission time associated with thepending transmission; comparing the transmission time with an amount oftime remaining before the first access point sleep interval begins;determining that the transmission time is greater than the amount oftime remaining before the first access point sleep interval begins; andpreventing execution of the pending transmission associated with thefirst station.
 24. The machine-readable storage media of claim 21,wherein the operations further comprise: receiving a second message atthe access point from a second station, via the wireless communicationchannel, indicating a second station sleep interval associated with thesecond station, wherein the second station sleep interval indicates atime interval for which the second station will enter a sleep mode;calculating a second access point quiet information comprising a secondaccess point sleep interval based, at least in part, on the firststation sleep interval and the second station sleep interval, whereinthe second access point sleep interval indicates a time interval forwhich the access point will enter a sleep mode; and transmitting to thefirst and the second stations, via the wireless communication channel, asecond beacon indicating the second access point quiet information toprevent the first and the second stations from initiating transmissionsto the access point during the second access point sleep interval. 25.The machine-readable storage media of claim 24, wherein said operationof calculating the second access point quiet information furthercomprises: determining a least common factor between the first stationsleep interval associated with the first station and the second stationsleep interval associated with the second station; and determining whento initiate the second access point sleep interval based, at least inpart, on said determining the least common factor between the firststation sleep interval associated with the first station and the secondstation sleep interval associated with the second station.